Method of recording and reproducing data on a disk

ABSTRACT

In recording data on a rewritable optical disk with a mark edge recording method, the occurrence of edge shift is compensated for. As a first power of a laser beam is greater than a second power, start and termination ends of each mark are produced by irradiation of the first power and a remaining intermediate portion of the mark is produced by irradiating the first and second powers alternately at equal intervals of a predetermined duration which is shorter than a period of a clock pulse. Also, the start and termination ends of the mark are specifically dislocated corresponding to a length of the mark and lengths of two neighbor spaces before and after the mark.

This application is a divisional of allowed application Ser. No.08/222,578, now U.S. Pat. No. 5,490,296 filed in the U.S. Patent andTrademark Office on Apr. 4, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Inventions

The present invention relates to a method of recording data on anoptical rewritable disk using a mark edge recording method and to anapparatus for recording and reproducing the recorded data, and moreparticularly, to compensation on recording data in order to correctlyread recording marks in the form of pulse trains and mark edge positionsof a reproduced signal.

2. Description of the Prior Art

One of the advanced disk-shaped recording mediums capable of storingdata at high density is known as a phase-change optical disk. Data canbe recorded on the phase-change optical disk by irradiating a surface ofan optical disk being rotated with a converged laser beam to heat up andmelt the irradiated area of a recording layer. A difference of the powerof the recording laser beam causes differences of the recording layer inarrival temperature and cooling process, and in turn causes a differencein the physical state or phase, of the recording layer. Morespecifically, an area irradiated with a high power laser beam becomeshigh in temperature and then cools down rapidly to become an amorphousphase. On the other hand, an area irradiated with a relatively low powerlaser beam becomes moderate in temperature and then cools down graduallyto become a crystal-line phase. The amorphous area is commonly called asa mark and the crystallized area is called as a space. In recording,binary data is stored in a series of marks and spaces. It is alsopossible for the phase-change optical disk to erase old data and recordnew data simultaneously using a single laser beam, or to perform directoverwriting operations.

In reproduction, a lower power laser beam whose power is too low toinduce a phase change irradiates the recording layer and its reflectedbeam is detected. Since the reflectivity is low on the amorphous markand high on the crystallized space, a difference in the intensity of thereflects beam between the mark and the space is detected to obtain areproduced signal.

Recording of data on phase-change optical disks is generally carried outby two known methods, a mark position recording method (MPR) and a markedge recording method (MER). The MPR method records marks of a short,uniform length at different intervals so that the position of the markscorrespond to the data. In the MER method, marks of different lengthsare recorded at different intervals so that the start and terminationedges of each mark correspond to the data. Accordingly, the MER methodcan generally record at a higher data density than the MPR method. Thereis generally an edge shift which is a difference of the position of anedge of the reproduced signal from its ideal position. As the edgescorrespond to the data in the MER method, the edge shift causes anincrease in the error rate of the reproduced signal in the MER method.It is thus essential for realization of the high density recording inthe MER method to accurately arrange the edges of each mark so as to beat their desired locations.

In the MER method marks having a greater length are recorded as comparedwith those of the MPR method. However, it is common on the phase-changeoptical disk for a rear half of each mark to become wide in width in aradial direction due to a heat storage effect of the recording layerwhen a long mark has been recorded by irradiation of a uniform laserbeam. This event will lead to incomplete erasing in direct overwritingor crosstalk between tracks during reproduction, impairing therecording/reproducing characteristics. For preventing the width of themark from becoming wider in the radial direction in the rear half of themark, techniques have been introduced in which the power of the laserbeam is lessened at the rear half of each mark by controlling the powerof the laser beam or the recording pulse width so that the width of themark is uniform (for example, see Japanese Laid-open Patent PublicationsNos. 5-151638 and 3-185628).

There is substantial a disadvantage of those techniques. As described,the marks on a phase-change optical disk are lower in reflectivity oflight than the spaces whereby a difference in absorption of the light iscreated between the marks and the spaces. Also, heat for melting theamorphous phase portion is different from the heat for melting thecrystalline phase portion. In direct overwriting, when new data isrecorded on an existing mark or space with an equal intensity of laserbeam, edges of a new mark are changed in location because of differencesin absorbed energy and the arrival temperature. Particularly, when theirradiation of the laser is lowered at the rear half of the mark for theimprovement in the shape of the mark during recording, the amorphousphase of the rear half of the mark tends to be unstable, thus producingthe edge shift of a termination end of the mark during the directoverwriting.

In addition, three more disadvantages are developed when the marks andthe spaces are minimized in size for a high density recording. Firstly,a shorter length of the space produces thermal interference in that heatat the termination end crosses the space to increase temperature of astart end of a succeeding mark and heat at the start end of thesucceeding mark affects the cooling process of the termination end ofthe mark. Such thermal interference causes a change in the location ofthe edges of the mark. Secondly, since the mark with a shorter length isproduced by heating a smaller region of the recording layer as comparedwith the mark with a longer length, a length of the mark tends to beunproportional to a length of a corresponding signal data to be recordedbecause of the change of condition of the heat radiation. Hence, therecording conditions based on the marks with the longer length canhardly be implemented with the marks with the shorter length. Thirdly,it is also common that even if the marks and the spaces are recorded attheir correct locations on the phase-change optical disk, the positionsof the edges of the marks or the spaces with the shorter length areincorrectly reproduced because the frequency characteristic decrease ata high frequency in a reproducing optical system. The frequencycharacteristics during reproducing may be equalized so as not to causethe edge shift. However, this does not conform to a favorablerequirement that the reproduced signal have an improved S/N(signal-to-noise) ratio so as to have less noise. In other words, theedge shift will increase as the S/N ratio is being enhanced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ifrecording data on a disk in which a width of each long mark issubstantially uniform, and in which an edge shift generated at antermination end of a mark during direct overwriting is minimized, and inwhich the occurrence of the edge shift caused by thermal interferenceacross a shorter space in recording, the nonlinearity of a short mark,and the equalization characteristics during recording are compensatedfor. The first power and a second power alternately at equal intervalsof a duration which is shorter than a period of a data clock signal inthe remaining intermediate portion of the mark, where the first power ishigher than the second power. To obtain the third feature, another diskdata recording method according to the present invention is provided inwhich positions of the start and termination ends of each mark arechanged according to a length of the mark and lengths of two neighborspaces before and after the mark.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a data to be recorded, a laser irradiationintensity, and a arrangement according to a disk data recording methodof the present invention.

FIG. 2 is a block diagram of a disk data recording apparatus showing oneembodiment of the present invention.

FIG. 3 is a waveform diagram of respective signals explaining the actionof the embodiment of the present invention.

FIG. 4 is a schematic view of a first example of a laser diode drivercircuit.

FIG. 5 is a schematic view of a second example of the laser diode drivercircuit.

FIG. 6 is a block diagram of a disk data reproducing apparatus showinganother embodiment of the present invention.

FIG. 7 is a block diagram of a disk data recording/reproducing apparatusshowing a further embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus in accordance with one embodiment of the present inventionemploys a rewritable phase-change optical disk for recording a digitalform of binary data in a mark/space format as assigning its binary bitshift to both edges of a mark. For recording such data on a phase-changeoptical disk, two different laser beams are used; a first power beam forchanging regions of a recording layer to an amorphous phase to createmarks and thus termed as a recording power beam, and a second power beamfor changing the same to a crystalline phase to erase the marks andtermed as an erasing power beam.

FIG. 1 shows the data (a) to be recorded, a laser irradiation intensity(b) after relevant compensation, and a mark arrangement (c) produced ona disk, explaining a disk data recording in accordance with the presentinvention. More specifically, the recording power of the presentinvention is applied for a predetermined duration to form start andtermination ends of each mark respectively without correspondingdirectly to a waveform of a recording data and two, recording anderasing, powers are alternately irradiated at short intervals to form anintermediate portion of the mark. Accordingly, unwanted overheating at atermination end of the mark is prevented and also, the mark issubstantially uniform in width even if it has a considerable length. Asthe termination end of the mark is sufficiently heated by irradiation ofthe recording power for the predetermined duration, it will be lessaffected by the behavior of an existing phase during recording or itsedge location will hardly be changed in direct overwriting.

It is desired that an irradiation duration of the recording power forthe start and termination ends is equal to a period of a clock signalfor ease of implementation. Alteration of the two powers on theintermediate portion of the mark is preferably at equal intervals of aduration which is shorter than the period of the clock signal to preventa mark width from varying in proportion to the alteration of the twopowers. More preferably, an interval of the alteration is one halfperiod of the clock signal as being easily initiated therefrom.

Since the start and termination ends of the mark are recordedcorresponding to a length of the mark and lengths of two neighboringspaces before and after the mark, the occurrence of edge shift caused bythermal interference across a shorter space, thermal nonlinearity of ashorter mark, and other reproduction characteristics can be compensatedfor. The edge shift appears frequently when the length of the mark or aspace is smaller than a given value. It is very rare to displace an edgeof a mark with a greater length than the given value. Accordingly, themarks to be recorded are correctly effectively implemented bymaintaining the start and termination ends of each mark at theirlocations when its length or a length of any adjacent space is notsmaller than the given value and dislocating them when the length or thelength of any adjacent space is smaller than the given value. The givenvalue of a limit length may vary depending on a in accordance with datamodulation, a structure of the recording layer of the disk, and arecording density. In practice, effective recording is possible bydislocating the position of the start and termination ends of a shortestmark or space in the data to be recorded as well as a second shortestmark or space.

A disk recording apparatus in accordance with the present invention isdescribed in detail below referring to relevant drawings. FIG. 2 shows ablock diagram of a disk data recording apparatus and FIG. 3 is awaveform diagram of respective signals used in the disk data recordingapparatus.

Referring to FIG. 2, data 1 to be recorded, a start end pulse generatorcircuit 2, a start end pulse 3, a burst gate signal generator circuit 4,a burst gate signal 5, a termination end pulse generator circuit 6, atermination end pulse 7, a mark/space length detector circuit 8, a 2Tmark signal 9, a 2T space signal 10, an encoder 11, a select signal 12,start end position data 13, a start end selector 14, a selected startend position data 15, a start end sample/hold circuit 16, a hold startend position data 36, a start end programmable delay line 17, a delayedstart end pulse 18, termination end position data 19, a termination endselector 20, a selected termination end position data 21, a terminationend sample/hold circuit 22, a hold termination end position data 35, atermination end programmable delay line 23, a delayed termination endpulse 24, a clock signal 25, an AND gate 26, a burst signal 27, an ORgate 28, a recording signal 29, a laser diode driver circuit 30, a laserbeam 31, an optical head 32, a phase-change optical disk 33, and aspindle motor 34 are provided.

As shown in FIG. 3, the letters a to n represent the data 1 to berecorded, the start end pulse 3, the burst gate signal 5, the clocksignal 25, the termination end pulse 7, the 2T mark signal 9, the 2Tspace signal 10, the select signal 12, the hold start end position data36, the delayed start end pulse 18, the hold training end position data35, the delayed termination end pulse 24, the burst signal 27, and therecoding signal 29 respectively specified in FIG. 2. Also, denoted by ois a row of marks and spaces recorded on the disk and p is a reproducedsignal reproduced by reading the marks and the spaces with acorresponding disk data reproducing apparatus. A reproduced data q isobtained by binarization of the reproduced signal at a slice level.

The operation is described below in more detail referring to FIG. 3. Thedata 1 is in a digital form comprising a stream of 1s and 0s which aretransmitted at a rate of a bit per clock period T with the least unit oftwo consecutive bits (see a of FIG. 3). The bits of the data 1 arerecorded in a form of marks and spaces on an optical disk; 1s allocatedto the marks and 0s allocated to the spaces. The start end pulse signal3 and the termination end pulse signal 7 have a pulse width equal to aclock period. The pulse width of the burst signal 27 is 1/2 the clockperiod. The mark/space length detector circuit 8 detects a mark or spacewhich is short enough to induce the edge shift in the high densityrecording. In this embodiment, the shortest length 2T of the mark or thespace in data records is a target to be detected.

The start end pulse generator circuit 2 generates the start end pulsesignal 3 of which pulse is assigned to a leading end of each 1-bit groupin the data 1 (shown as b). The burst gate signal generator circuit 4produces the burst gate signal 5 which has a pulse width (equivalent tothe length of the mark minus three clock periods) and is assigned to acenter of the mark or the 1-bit group (shown as c). Hence, if the lengthof the mark is less than 3 clock periods, no burst gate pulse isgenerated. The termination end generator circuit 6 produces thetermination end pulse signal 7 of which pulse is assigned to a trailingend of each 1-bit group (shown as e).

The mark/space length detector circuit 8 when detecting a mark or spaceof 2T length produces respectively a 2-clock-period pulse of the 2T marksignal 9 which comprises a start end pulse 102 and a termination endpulse 103 (shown as f) or a 4-clock-period pulse of the 2T space signal10 which includes two edge pulses 104 and 100 at the start andtermination ends of the 2T space (shown as g).

The encoder 11 then identifies attributes of the start end pulse signal3 and the termination end pulse signal 7 from the 2T mark signal 9 andthe 2T space signal 10 to deliver the select signal 12. It is assumedthat the attributes are classified to four distinct types: normal inwhich both the mark and the space are not shorter than 3T, 2Ts in whichthe mark is not shorter than 3T but the space equals 2T, 2Tm in whichthe space is not shorter than 3T but the mark is 2T, and 2Ts-2Tm inwhich both the mark and the space are equal to 2T. For example, thestart end pulse 100 shown in FIG. 3 falls in 2Ts, the termination endpulse 101 stays in normal, the start end pulse 102 falls in 2Tm, and thetermination end pulse 103 is defined by 2Ts-2Tm (shown in h).

According to the select signal 12, the start end selector 14 selectscorresponding one from the start end position data 13, that is,respective start end positions in normal duration, in 2Ts duration, in2Tm duration, and in 2Ts-2Tm duration, which is then transferred as theselected start end position data 15. The start end sample/hold circuit16 performs updating upon receiving the start end pulse signal 3 butholds a preceding piece of data when no start end pulse signal isloaded, and delivers a held start end position data 36 (shown as i). Thestart end programmable delay line 17 delays the start end pulse signal 3by a delay time determined by the hold start end position data 36 inorder to deliver the delayed start end pulse signal 18 (shown as j).

Similarly, the termination end selector 20 selects one of thetermination end position data 19 according to the select signal 12 andtransmits the selected termination end position data 19, as the selectedtermination end position data 21 to the termination end sample/holdcircuit 22 which performs updating upon receipt of the termination endpulse signal 7 but otherwise holds the preceding piece of data anddelivers the hold termination end position data 35 (shown as k). Thetermination end programmable delay line 23 retards the start end pulsesignal 3 by a delay time determined by the hold termination end positiondata 35 in order to deliver the delayed termination end pulse signal 24(shown as 1).

The AND gate 26 calculates a logic product from the burst gate signal 5and the clock signal 25 to generate the burst signal 27 (shown as m).The OR gate 28 determines a logic sum of the delayed start end pulsesignal 18, the burst signal 27, and the delayed termination end pulsesignal 24 to produce the recording signal 29 (shown as n).

In response to the recording signal 29, the laser diode driver circuit30 creates the laser beam 31 of binary format whose intensity ismodulated to the two, recording and erasing, powers corresponding tobinary data of the recording signal 29. The laser beam 31 is focused bythe optical head 32 to a spot of irradiation to form the row of marksand spaces (shown as o) on a surface of the phase-change optical disk 33which is rotated by the spindle motor 34.

As described, the disk data recording apparatus of the present inventionis capable of recording the row of marks and spaces corresponding to thedata 1 while dislocating the start and termination ends of the markdefined by its length and the lengths of the two neighboring spacesbefore and after the mark. In this embodiment, dislocation of positionsof edges of the mark is implemented by comparing the shortest 2T marksand spaces with reference length. It may be done with more accuracy whenthe second shortest marks and spaces of 3T long are similarly detectedand used for the dislocation of edge positions in addition.

Two preferred arrangements of the laser diode driver circuit 30 isexplained as follows. FIG. 4 is a schematic view of a first example ofthe laser diode driver circuit 30 employing an n-type laser diode 53.The n-type laser diode 53 has an anode grounded and is driven by acombination of a main current source 50 and a sub current source 51coupled in parallel. The main current source 50 supplies the laser diode53 with a current for emission of the erasing power and the sub currentsource 51 and the main current source 50 provide a current the maincurrent source 50 for emission of the recording power. The sub currentsource 51 is connected and disconnected by on/off action of a switch 52activated by the recording signal 29, thus providing two-level currentsto the laser diode 53. A resultant laser beam 31 outputted from thelaser diode driver circuit is directed to the optical head 32 forrecording.

FIG. 5 is a schematic view of a second example of the laser diode drivercircuit 30 in which a p-type laser diode 57 has a cathode grounded andis driven by a main current source 54. While a current output of themain current source 54 actuates the laser diode 57 for the emission ofthe recording power, its portion is drained out through a sub currentsource 55 to allow the laser diode 57 to generate the erasing power.With the sub current source 55 being connected and disconnected by theon/off action of a switch 56 conducted by the recording signal 29, acurrent to the laser diode 57 is modulated to two levels. The currentoutput of the main current source 54 for the emission of the recordingpower is reduced by a current value of the sub current source 55 toallow the laser diode 57 to emit the erasing power. A resultant laserbeam 31 of the binary form is transmitted to the optical recording head32.

FIG. 6 illustrates a disk data reproducing apparatus of anotherembodiment of the present invention for reproducing a reproduced signalfrom the data recorded on the disk. As shown, there are provided a disk200 on which the data are recorded, a spindle motor 201 for rotation ofthe disk 200, an optical head 202 for scanning the disk 200 to producethe reproduced signal, a preamplifier 203 for amplifying the reproducedsignal, an equalizer 204 for compensating for the frequencycharacteristic of the reproduced signal, and a comparator 205 forbinarizing the reproduced signal 208 with using of a slice level voltage206 to construct a reproduced data 207 are provided.

The reproduced signal 208 and the reproduced data 207 shown in FIG. 6are as denoted by p and q in FIG. 3 respectively. According to theanother embodiment, the reproduced data 207 (shown as q) has the samewaveform as of the data 1 (shown as a). The frequency characteristic ofthe equalizer 204 can offer a flat response and preferably, may bearranged so as to correct for the frequency characteristic of whichdecrease at a high frequency in a disk data reproduction system forminimizing the edge shift and to vary the frequency distribution ofnoise contained in the reproduced signal 208 for increasing the S/Nratio and then decreasing the error rate. It is, however, not easy tohave such an equalizer with two improvements: reduction in the edgeshift and increase in the S/N ratio.

The disk data recording apparatus of the present invention is capable ofassigning the start end position data 13 and the termination endposition data 19 to optimum values which match the frequencycharacteristic of the disk data reproducing apparatus. Accordingly,since the equalizer 204 provides the frequency characteristic forensuring an optimum S/N ratio of the reproduced signal, the edge shiftis compensated for by the disk data recording apparatus of the oneembodiment. As the result, the start end position data and thetermination end position data of the marks and the spaces to bereproduced can be detected at high accuracy with a minimum of noisejitter.

A disk data recording/reproducing apparatus of the present invention isdescribed as follows. FIG. 7 is a block diagram of the disk datarecording/reproducing apparatus in which components in FIG. 7 areidentical to those of the previous embodiments shown in FIGS. 2 and 6and they and their functions will not be explained in more detail. Asapparent, the disk data recording apparatus and the disk datareproducing apparatus of the two previous embodiments are combinedtogether so that the data can be recorded on and reproduced from theoptical disk. It is possible to perform the recording and reproducingactions separately or simultaneously. The optical record head 32 and theoptical reproduction head 202 may be replaced by a singlerecord/reproduction head which does not allow the recording andreproducing actions to be carried out at the same time.

Although the rewritable optical disk in the embodiments is aphase-change disk, it may be a magneto-optic disk. It is preferred tocarry out optical modulation recording on such magneto-optic disk usingtwo different laser beams of binary form: recording power and zero orreproducing power. The width of the start or termination end pulse isnot limited to a period of a clock pulse. It is advantageous to have apulse width of any relevant signal equal to the period of the clockpulse because such pulses are readily generated with a conventionalsynchronizing circuit which contributes to the minimum size of acircuitry arrangement. With a similar reason, the pulse width of theburst signal is preferably 1/2 the period of the clock pulse since itcan be produced directly from the clock signal.

What is claimed is:
 1. A disk data recording method for recording aninput data at a data clock signal having a specific clock period on adisk recording medium in a form of position information of leading andtrailing edges of marks with a laser beam, the input data being composedof alternately occurring mark data parts and space data parts, saidmethod comprising the steps of:generating a mark start end pulse for apredetermined period at a start end of a mark data part of the inputdata; generating a mark termination end pulse for the predeterminedperiod at a termination end of the mark data part; generating a train ofintermediate pulses occurring at equal intervals of a predeterminedduration; arranging in order the mark start end pulse, the train ofintermediate pulses and the mark termination end pulse to obtain arecording signal; driving a laser beam source according to the recordingsignal to produce a laser beam whose power becomes a first power for thepredetermined period at a portion corresponding the mark start end pulseand at a portion corresponding to the mark termination end pulse andbecomes the first power and a second power alternately at equalintervals of the predetermined duration at a portion corresponding tothe train of intermediate pulses; and irradiating the disk recordingmedium with the laser beam to form a mark, wherein said method furthercomprises a step of determining a position of the mark start end pulseaccording to both a length of a space data part immediately before themark data part and a length of the mark data part.
 2. A method accordingto claim 1, wherein said step of determining the position of the markstart end pulse includes delaying the position of the mark start endpulse when the length of the space data part immediately before the markdata part and the length of the mark data part are shorter than apredetermined length, and maintaining the position of mark start endpulse when the length of the space data part immediately before the markdata part and the length of the mark data part are not shorter than thepredetermined length.
 3. A method according to claim 1, furthercomprising a step of determining a position of the mark termination endpulse according to both a length of a space data part immediately afterthe mark data part and the length of the mark data part.
 4. A methodaccording to claim 3, wherein said step of determining the position ofthe mark termination end pulse includes delaying the position of themark termination end pulse when the length of the space data partimmediately after the mark data part and the length of the mark datapart are shorter than a predetermined length, and maintaining theposition of mark termination end pulse when the length of the space datapart immediately after the mark data part and the length of the markdata part are not shorter than the predetermined length.
 5. A methodaccording to claim 1, wherein the predetermined period is substantiallyequal to the clock period and the predetermined duration issubstantially equal to 1/2 the clock period.